Device for monitoring control elements

ABSTRACT

Device for monitoring the relative position of synchronously moved control elements, especially for monitoring the movement of two valve cases in safety valves controlling a pneumatic or hydraulic drive. The device includes a magnetic member disposed at each of the valve cases and symmetrically arranged with respect to one another, a rotatably mounted magnetic bar having each of the magnetic members arranged proximate to a free end thereof for magnetically influencing the positioning thereof. Spring forces and magnetic forces are effective on the bar so as to provide the bar with a first basic stable position corresponding to synchronous movement of the valve cases and two stable disturbance positions corresponding to asynchronous movement of the valve cases.

United States Patent 1 1 Stahle June 4, 1974 [5 DEVICE FOR MONITORINGCONTROL 2.575.086 11/1951 Atchison 200/83 L ELEMENTS 2.869,475 1/1959Bobo 200/83 L 3,562,455 2/1971 McQueen ZOO/8L9 M [75] lnventor: KurtStahle, Steinegg, Germany [73] Assignee: Concordia Maschinenund maryExaminer-Harold Broome El ktrizimt -G bfl, St t Attorney, Agent, orFirm-Craig and Antonelli Germany 22 Filed: Jan. 26, 1973 [571 ABSTRACT[211 App] No 327 165 Device for monitoring the relative position ofsynchronously moved control elements, especially for monitoring themovement of two valve cases in safety [30] Foreign Application PriorityData valves controlling a pneumatic or hydraulic drive. The Jan. 25.1972 Germany 2203266 device includes magnetic member disposed at each ofthe valve cases and symmetrically arranged with re- [52] US. Cl. 335/1,ZOO/82E, 335/ 177, spect to one another, ably mounted magnetic '335/236bar having each of the magnetic members arranged 511 1m. (:1. HOlh 9/00proximate to a free end thereof for magnetically influ- [58] Field ofSearch ZOO/81.9 M, 82 E, 83 L; c g the positioning thereof. Springforces and mag- 335 20 207 205 259 3 125 7 237 netic forces areeffective on the bar so as to provide 174, 1, 2 177, 236 the bar withafirst basic stable position corresponding to synchronous movement ofthe valve cases and two [56] References Cit d stable disturbancepositions corresponding to asyn- UNITED STATES PATENTS 8/l905 Sundh335/183 chronous movement of the valve cases.

23 Claims, 4 Drawing Figures 1 DEVICE FOR MONITORING CONTROL ELEMENTSThe present invention relates to a device for the monitoring of therelative position of synchronously moved control elements, in particularfor the monitoring of the movement of two valve cases in safety valvesfor the control of pneumatic or hydraulic drives.

Many different types of constructions of monitoring devices for safetyvalves are known. Thus, there are arrangements, for example, wherein amechanical coupling of the two valve cases is provided with the aid of athin wire attached to extensions on the valve cases, the wire havingcurrent flowing 'therethrough and ruptures in case of an asynchronousmovement, thus interrupting the monitoring circuit. However, suchmonitoring devices have the disadvantage that a new'safety wire must beinstalled in each case in order to return the mechanism into theoperative condition, which is very time-consuming and cumbersome andunnecessarily prolongs the time for. placing the device or monitoredequipment back into operation, even though the actual error had beenfound very quickly.

Another known mechanical solution (French Pat. No. 1,292,283) disposes across member between the two valve stems, in place of a safety wire,with a plunger being displaceably arranged in the cross membet. Theplunger, on the one hand, is in engagement with an electrical switchingcontact and, on the other hand, via an interposed ball, contacts agroove of a valve stem, so that it is displaced in case of a nonuniformoperation of the valve stems and can cut off the drive via the switchingcontact. This solution has the disadvantage of being extremelytrouble-prone, since the plunger can easily jam. Also, the responseaccuracy is relatively low, due to the selected mechanical trippingarrangement.

Other mechanical monitoring mechanisms have been proposed (DAS Pat. No.1,294,8l8) wherein the free ends of the valve stems contact a rockerplate via springs such that the position of this plate remainsunaffected during ordinary operation, with the plate being pivoted onlyin case of an asynchronous operation of the valve stems and triggering aswitching Contact via a cam disposed in the center thereof. In thisarrangement,the response accuracy as inthe other monitoring devices isalso not very high. In particular, difficulties are to be expected inthe monitoring safety, because the two springs utilized exhibit agingphenomena, primarily after a longer operating period due to the constantstress, resulting in erroneous indication of disturbances. Additionally,there is the difficulty of being able to adapt the characteristics ofboth springs to each other in such a manner that the forces exerted bythe valve stems on the rocker plate at each stroke are always equallylarge.

It has also been known to effect the monitoring of the .synchronousmovement by means of a pneumatic couin impairing the safe operation ofthe monitoring device in some instances, thus leading to interruptionsof the operation even if there is no actual flaw in the valve systemproper.

Therefore, it is an object of the present invention to avoid thedisadvantages of the prior art devices and to provide a monitoringdevice which is maximally simple and service-free and yet has theproperties to effect an interruption of the operation in case an erroroccurs and a quick return to operation after the flaw has been located.

The present invention provides a monitoring device having an elementconsisting of a magnetic material fixedly attached to each valve case,these elements being arranged in symmetry to each other. Each element isdisposed in the zone of the free ends of a rotatably mounted magneticbar for magneticallyinflueno ing the bar. The magnetic bar is adjusted,in its basic position, to the synchronous position of the valve casesand triggers a signal for the inactivation of the drive upon rotationout of the basic position. This arrangement makes it possible to providethat, when the two valve cases are Operating synchronously, the magneticforces exerted on the magnetic bar at both ends are respectively equallylarge, so that the position of the magnetic bar remains unaffected. lncontradistinction, when the operation is asynchronous, the magnetic baris moved out of its basic position, and this deflected motion of themagnetic bar can be utilized for triggering a pulse for error indicationand, for example, also for shutting off the control valve and thusrender a press inoperative. The novel monitoring device can beconstructed without wear-prone parts and thus is service-free to anunlimited extent. Additionally, the device can be designed to berelatively simple and thus inexpensive.

According to a feature of the present invention, the magnetic bar ismaintained in its basic position by means of spring force, so that themonitoring device becomes independent of location. In order to providelarge magnetic forces in a maximally simple manner, the magnetic bar canconsist of soft iron and can be disposed in a magnetic member whichannularly surrounds the magnetic bar. This magnetic member can be, forexample, an electromagnetic coil. However, in anespecially simplemanner, a permanent magnet is provided as the magnetic member and isfashioned as an annular closed soft-iron bridge member. According toanother feature of the invention, a torsion rod is arranged for themonitoring of the magnetic bar so that wear of the parts due to frictiondoes not occur.

In accordance with a further feature of the present invention, toprovide for the triggering of an errordetection pulse, the magnetic baris arranged to engage plungers on both sides of its fulcrum. whichplungers are connected to electric switches. Each rotational deflectionof the bar thus triggers a switching process. In this connection, it isespecially advantageous to adapt the spring force of the torsion rod tothe magnetic forces in such a manner that the magnetic bar has a basicstable position determined by the spring force and two disturbancepositions determined by the magnetic forces from which disturbancepositions the magnetic bar can be returned into the basic position onlyby a separate switching step. This arrangement fulfills the prerequisitethat, in case of a disturbance, the valve cannot be returned tooperation until a separate switching process is triggered afterelimination of the trouble. In this Connection, it has been foundthat,due to the square force characteristics of the magnetic forces, twochangeover points result in the movement of the magnetic bar from whichthe stable basic position into the respective disturbance positions,which are again stable, and that, because of this property, the magneticbar is deflected, after passing the changeover points, suddenly, ratherthan gradually, so that high-power limit switches can be connected tothe actuating plungers. The provision of microswitches and theadditional arrangement of heavy-duty switches are thus eliminated.Finally, in safety valves having electromagnetically operated auxiliarycontrol valves for the valve cases, provision can be made for restoringthe magnetic bar into the basic position by arranging a shortcircuitingswitch bridging the electrical switches in contact with the plungers andbeing located in the circuit of the auxiliary valves. Thisshort-circuiting switch, upon its actuation, serves for placing bothvalve cases into a synchronous position and thus effects a restorationof the magnetic bar into the basic position by the thus-producedpredominance of the restoring spring forces. 1

These and further objects, features and advantages of the presentinvention will become more obvious from the following description whentaken in connection with the accompanying drawings which show, forpurposes of illustration only, several embodiments in accordance withthe present invention, and wherein FIG. I is a schematic cross-sectionalview through a safety valve having a monitoring device according to thepresent invention;

FIG. 2 is an enlarged partial cross-sectional view of the monitoringdevice in the basic'operating position, wherein the left-hand andrighbhand halves of the figure illustrate different possibilities forthe construction of the magnetic bar;

FIG. 3 shows the monitoring deviceof FIG. 2 in the disturbance position;and

FIG. 4 is a diagram representing the force relationship at the magneticbar of the monitoring device.

Referring now to the drawing wherein like reference numerals designatelike parts throughout the several views, there is shown in FIG. 1, twovalve cases 2 and 3 disposed within the housing 1 of a safety valve.Each valve case comprises a valve stem 2a and 3a respectively, a valveelement 4 having the shape of a piston, and a disk valve member 5attached to the valve stem. The valve cases 2 and 3 are arranged withinthe housing 1 in such a manner that they respectively close or uncovervalve seats 6 and 7 during their upward and downward movement. The valveseats connect an upper pressure medium chamber 8 and a lower pressuremedium chamber 9 with each other; the chambers being charged with thepressure medium in a conventional manner not illustrated in detail.

In the illustrated position, the valve disks 5 respectively seal thelower valve seat 7, so that the communication between the chambers 8 and9 is interrupted. When introducing pressure medium into the space 10respectively located above each of the pistons 4, the valve cases 2 and3 move downwardly 'such that the disks 5 free the valve seats and thepressure chambers 8 and 9 are placed in communication with'each other.The feed and discharge ducts of the pressure medium into and out of thechambers 8 and 9 are provided in the conventional manner and thereforeare not shown. The pressure medium passes into the spaces 10 above thepistons 4 via auxiliary control valves 11 which are controlledelectromagnetically and are connected in a circuit 12 wherein twoswitches 13 are disposed as will be discussed below.

Valves of the illustrated type are utilized, for example, for thecontrol of hydraulic presses where a flawless functioning of the valveis important, for example in order to exclude injury to the operatingpersonnel. For this purpose, the two valve cases 2 and 3 are'connectedin parallel, so that even if one valve case should become inoperativedue to a flaw, the faultless functioning of the safety valve is stillensured. A prerequisite therefor is that the valve cases 2 and 3 areeach moved synchronously and, in case this synchronous movement isabsent, a disturbance signal is triggered which controls the machineconnected thereto, for example the hydraulic press, to render the sameinoperative. In accordance with safety regulations, it must be ensuredthat the press can be'placed back into operation only after the flaw atthe valve or also at the feed line thereto has been repaired.

In order to monitor the synchronous operation of the valve cases 2 and3, a monitoring devicel4 is provided which comprises a magnetic bar 16mounted at a torsion rod 15 and a permanent magnet fashioned as asoft-iron bridge 17. The permanent magnet, as can be seen particularlyfrom FIG. 2 is provided with apertures 18 with extensions 19 of thevalve stems 2a and 30 extending into these apertures, the extensionsbeing made of a magnetic material. The magnetic bar 16 can have aconfiguration, as shown in the left-hand portion of FIG. 2, such thatthe extensions 19 sweep past the ends thereof. Alternatively, asillustrated in the righthand portion, the magnetic bar can also beprovided with bores 16a at both of its ends such that the exten sions 19enter these bores and canthus exert a stronger magnetic effect. Themagnetic bar 16 is held in its basic position shown in FIG. 2 by thespring force of the torsion rod 15, on the one hand, and also by the twoplungers 20, on the other hand, under the biasing effect of the springs21 which press the plungers 20 against the magnetic bar 16 and keep theswitches 13, mentioned above, in the closed position.

During synchronous operation of the safety valve, the position of themagnetic bar 16 according to FIG. 2 remains unchanged because the forcesexerted onthe magnetic bar by the permanent magnet 17 and the extensions19 moved therein are equally large at both ends of the bar 16. Theswitches 13 therefore remain closed, and the spaces 10 (FIG. 1) can eachbe charged with the pressure medium in a controlled rhythm.

'Incase an error or disturbance occurs such that the valve cases 2 and 3do not move in synchronism, the left extension 19, for example, will beshifted at the stem 2a farther downwardly than the right extension 19 ofthe stem 3a, as illustrated in FIG. 3. Due to this asymmetry, themagnetic flux at the left end of the magnetic bar 16 is larger than themagnetic flux at the right end of the magnetic bar 16 such that a forceis effective on the magnetic bar 16 in the direction of arrow 21, andthe magnetic bar is rotated by the angle (b from its basic position intothe disturbance position according to FIG. 3. The manner in which thisrotation takes place and the effects of the forces are described indetail hereinbelow with reference to FIG. 4. As shown in FIG. 3, by therotation of the magnetic bar 16, the right-hand plunger is presseddownwardly, so that the right-hand switch in FIG. 1 is opened andinterrupts the circuit to the auxiliary valves 11. This interrupts thefeed of pressure medium to the spaces 10, and both valve cases 2 and 3return into their initial position shown in FIG. 1, wherein there is nocommunication between chambers 8 and 9. In this position, no operatingpressure medium flows from the valve to the machine connected thereto,i.e., no pressure medium is fed to the press cylinder such that thepress ramwould likewise return into the initial position.

The safety valve as well as the press ram remain in the initial positionuntil the flaw has been corrected and the two valve cases 2 and 3 havereturned into their synchronous position and/or the magnetic bar hasbeen returned to its basic position as shown in FIG. 2. The resetting,in case of valves of the type shown in FIG. 1, i.e., in case of valveshaving electromagnetically controlled auxiliary valves, can be effectedin a very simple manner by providing an additional switch 22 as shown inFIG. I disposed in a short-circuit branch line 23 connected to thecircuit 12 and bridging the two switches After having explained the modeof operation of the monitoring device of the present invention in itsbasic aspects, a detailed discussion of the switching procedureinvolving the magnetic bar 16 will now be provided with reference toFIG. 4. In FIG. 4, the axis K is used for plotting the forces effectiveon the magnetic bar 16, which latter acts as a type of armature in themagnetic system. Among the forces effective on the magnetic bar 16,there are first of all the spring forces denoted by f, which are shownas a full line and which linearly increase with increasing twistingangle 5. These spring forces are composed, in the illustrated example,of the spring force of the torsion rod 15 and of the forces of thesprings 21 effective on the magnetic bar. The magnetic forces m, shownin dot-dash lines and having a square force characteristic, act inopposition to the spring forces. It can be seen from the diagram thatthe spring forces f effective oppositely to the magnetic forces m arestill larger, within a certain twistingangle 45, than the magneticforces m, and the curve f-m passes through zero in a point P wherein thedifference of the spring forces and the magnetic forces is zero, andfrom this point, with increasing 4:, the magnetic forces greatlyincrease. Thus, the rotational movement of the magnetic bar 16 up to thechangeover point P is within a tolerance range for the maximallypermissible deviation from the synchronous movement, but that thereaftera sudden rotational movement is effected. As such, rather than utilizemicroswitches for the switches 13, simpler heavy-duty switches can beemployed.

On the basis of these force relationships, the magnetic bar 16 isprovided with one stable basic position g, namely for all angles ofrotation between the two changeover points P and with two stabledisturbance positions in the ranges s between the angle at thechangeover point P and the respectively external abutment position.Consequently, the device of the present invention makes it possible witha corresponding dimensioning of the springs and the torsion rod 15 andan appropriate design of the magnetic forces, to eliminate the need forcomplicated sensing and scanning elements, or the arrangement ofspecial, sensitive switches, since the construction of the presentinvention is excellently suitable, in spite of its sensitive monitoringaction, for delivering mechanical forces readily sufficient for theoperation of heavy-duty switches. By the provision of means forlessening the spring force instead of the torsion rod 15, or by makingthe springs 2] adjustable, it is also possible to render the changeoverpoint of the monitoring device adjustable. This, then, also affords apossibility for adjusting the permissible deviation of the valve stempositions.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It should therefore beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

I claim:

1. Device for monitoring the relative position of two movable elementsarranged for corresponding synchronous movement, said device comprisinga first magnetic member arranged on each of said movable elements andsymmetrically disposed with respect to one another, magnetic bar meansmounted for rotational A movement and having a respective one of saidfirst magnetic members arranged proximate to a respective free endthereof for magnetically influencing the positioning of said magneticbar means, said magnetic bar means having a first basic positioncorresponding to the synchronous positioning of said movable elementsand being rotatable from the first basic position in response toasynchronous movement of said movable elements, and means responsive tothe movement of said magnetic bar means for providing an indication ofthe asynchronous movement of said movable elements.

2. A monitoring device according to claim 1, further comprising springforce means for biasing said magnetic bar means into the first basicposition thereof.

3. A monitoring device according to claim 1, wherein said magnetic barmeans is a soft iron bar and a second magnetic member annularlysurrounds said magnetic bar means, said magnetic bar means beingdisposed within said second magnetic member.

4. A monitoring device according to claim 3, wherein said secondmagnetic member is a permanent magnet and is constructed as an annularclosed soft iron bridge member.

5. A monitoring device according to claim 1, further comprising torsionrod means for rotatably mounting said magnetic bar means.

6. A monitoring device according to claim 1, wherein said meansresponsive to the movement of said magnetic bar means comprises meansfor providing an output signal indicative of such movement includingplunger means arranged for contacting said magnetic bar means proximateto each end thereof and switch means arranged in an electrical circuitmeans, said switch means being responsive to the movement of saidplunger means for triggering an output signal in said circuit means.

7. A monitoring device according to claim 2 wherein said magnetic barmeans is positioned in accordance with the magnetic forces and springforces effective thereon, said spring force means providing springforces coordinated with the magnetic forces so as to provide the firstbasic stable position of said magnetic bar means corresponding tosynchronous positioning of said movable elements within predeterminedlimits, and the magnetic forces effective on said magnetic bar meansovercoming the spring forces in response to asynchronous movement ofsaid movable elements to I provide two disturbance stable positions forsaid mag netic bar means.

8. A monitoring device according to claim 7, further comprisingswitching means effective for returning said magnetic bar means from oneof the stable disturbance positions to the first basic stable positionsthereof.

9. A monitoring device according to claim 7, wherein said magnetic barmeans is only responsive to switching means effective for returning saidmagnetic bar means from one of the stable disturbance positions to thefirst basic stable position thereof.

10. A monitoring device according to claim 1, wherein said two movableelements are two valve means of a safety valve for controlling one of apneumatic or hydraulic drive.

11. A monitoring device according to claim 10, wherein said two valvemeans each include a movable valve stem means and said first magneticmember is fixedly arranged on said valve stem and extends therefrom.

12. A monitoring device according to claim 11, wherein said magnetic barmeans is provided with an aperture means approximate to each free endthereof, and said aperture means is arranged for receiving one of saidfirst magnetic members extending from said valve stem means.

13. A monitoring device according to claim 11, wherein said means forindicating the asynchronous movement of said movable elements includesmeans for triggering a signal for shutting off the drive which iscontrolled.

14. A monitoring device according to claim 13, wherein said means fortriggering a signal include plunger means arranged for contacting saidmagnetic bar means proximate to each end thereof and switch meansarranged in a circuit and being responsive to the movement of saidplunger means for triggering a signal when said magnetic bar means movesfrom the first basic position thereof.

15. A monitoring device according to claim 10, further comprising springforce ,means for biasing said magnetic bar means into the basic positionthereof.

16. A monitoring device according to claim 15, wherein said magnetic barmeans is a soft iron bar and a second magnetic member annularlysurrounds said 8 magnet and is constructed as an annular closed, softiron bridge member.

18. A monitoring device according to claim 17,

wherein said permanent magnet is provided with a plurality of aperturemeans and said first magnetic members extending from said valve meansextend through respective ones of said aperture means into the regionproximate to the free ends of said magnetic bar means.

19. A monitoring device according to claim 10, further comprisingtorsion rod means for rotatably mounting said magnetic bar means.

20. A monitoring device according to claim 11, wherein said means forproviding an indication of the asynchronous movement of said movableelements comprises means for triggering a signal for shutting off thedrive which is controlled and includes plunger means arranged forcontacting said magnetic bar means proximate to each end thereof, andswitch means arranged in a circuit means and responsive to the movementof said plunger means, said plunger means actuating said switch means inresponse to movement of said magnetic bar means from the basic positionthereof.

21. A monitoring device according to claim 20, wherein said magentic barmeans is positioned in accordance with the magnetic forces and springforces effective thereon, said spring force means providing springforces coordinated with the magnetic forces so as to provide the firstbasic stable position of said magnetic bar means corresponding tosynchronous positioning of said valve means within predetermined limits,and the magnetic forces effective on said magnetic bar means overcomingthe spring forces in response to asynchronous movement of said valvemeans to provide two stable disturbance positions for said magnetic barmeans.

22. A monitoring device according to claim 21, further comprisingswitching means effective for returning said magnetic bar means from oneof the stable disturbance positions thereof to the first basic stableposition bar, said bar being disposed within said second magneticmember.

17. A monitoring device according to claim 16, wherein said secondmagnetic member is a permanent circuit means of said auxiliary controlvalve means.

1. Device for monitoring the relative position of two movable elementsarranged for corresponding synchronous movement, said device comprisinga first magnetic member arranged on each of said movable elements andsymmetrically disposed with respect to one another, magnetic bar meansmounted for rotational movement and having a respective one of saidfirst magnetic members arranged proximate to a respective free endthereof for magnetically influencing the positioning of said magneticbar means, said magnetic bar means having a first basic positioncorresponding to the synchronous positioning of said movable elementsand being rotatable from the first basic position in response toasynchronous movement of said movable elements, and means responsive tothe movement of said magnetic bar means for providing an indication ofthe asynchronous movement of said movable elements.
 2. A monitoringdevice according to claim 1, further comprising spring force means forbiasing said magnetic bar means into the first basic position thereof.3. A monitoring device according to claim 1, wherein said magnetic barmeans is a soft iron bar and a second magnetic member annularlysurrounds said magnetic bar means, said magnetic bar means beingdisposed within said second magnetic member.
 4. A monitoring deviceaccording to claim 3, wherein said second magnetic member is a permanentmagnet and is constructed as an annular closed soft iron bridge member.5. A monitoring device according to claim 1, further comprising torsionrod means for rotatably mounting said magnetic bar means.
 6. Amonitoring device according to claim 1, wherein said means responsive tothe movement of said magnetic bar means comprises means for providing anoutput signal indicative of such movement including plunger meansarranged for contacting said magnetic bar means proximate to each endthereof and switch means arranged in an electrical circuit means, saidswitch means being responsive to the movement of said plunger means fortriggering an output signal in said circuit means.
 7. A monitoringdevice according to claim 2, wherein said magnetic bar means ispositioned in accordance with the magnetic forces and spring forceseffective thereon, said spring force means providing spring forcescoordinated with the magnetic forces so as to provide the first basicstable position of said magnetic bar means corresponding to synchronouspositioning of said movable elements within predetermined limits, andthe magnetic forces effective on said magnetic bar means overcoming thespring forces in response to asynchronous movement of said movableelements to provide two disturbance stable positions for said magneticbar means.
 8. A monitoring device according to claim 7, furthercomprising switching means effective for returning said magnetic barmeans from one of the stable disturbance positions to the first basicstable positions thereof.
 9. A monitoring device according to claim 7,wherein said magnetic bar means is only responsive to switching meanseffective for returning said magnetic bar means from one of the stabledisturbance positions to the first basic stable position thereof.
 10. Amonitoring device according to claim 1, wherein said two movableelements are two valve means of a safety valve for controlling one of apneumatic or hydraulic drive.
 11. A monitoring device according to claim10, wherein said two valve means each include a movable valve stem meansand said first magnetic member is fixedly arranged on said valve stemand extends therefrom.
 12. A monitoring device according to claim 11,wherein said magnetic bar means is provided with an aperture meansapproximate to each free end thereof, and said aperture means isarranged for receiving one of said first magnetic members extending fromsaid valve stem means.
 13. A monitoring device according to claim 11,wherein said means for indicating the asynchronous movement of saidmovable elements includes means for triggering a signal for shutting offthe drive which is controlled.
 14. A monitoring device according toclaim 13, wherein said means for triggering a signal include plungermeans arranged for contacting said magnetic bar means proximate to eachend thereof and switch means arranged in a circuit and being responsiveto the movement of said plunger means for triggering a signal when saidmagnetic bar means moves from the first basic position thereof.
 15. Amonitoring device according to claim 10, further comprising spring forcemeans for biasing said magnetic bar means into the basic positionthereof.
 16. A monitoring device according to claim 15, wherein saidmagnetic bar means is a soft iron bar and a second magnetic memberannularly surrounds said bar, said bar being disposed within said secondmagnetic member.
 17. A monitoring device according to claim 16, whereinsaid second magnetic member is a permanent magnet and is constructed asan annular closed, soft iron bridge member.
 18. A monitoring deviceaccording to claim 17, wherein said permanent magnet is provided with aplurality of aperture means and said first magnetic members extendingfrom said valve means extend through respective ones of said aperturemeans into the region proximate to the free ends of said magnetic barmeans.
 19. A monitoring device according to claim 10, further comprisingtorsion rod means for rotatably mounting said magnetic bar means.
 20. Amonitoring device according to claim 11, wherein said means forproviding an indication of the asynchronous movement of said movableelements comprises means for triggering a signal for shutting off thedrive which is controlled and includes plunger means arranged forcontacting said magnetic bar means proximate to each end thereof, andswitch means arranged in a circuit means and responsive to the movementof said plunger means, said plunger means actuating said switch means inresponse to movement of said magnetic bar means from the basic positionthereof.
 21. A monitoring device according to claim 20, wherein saidmagentic bar means is positioned in accordance with the magnetic forcesand spring forces effective thereon, said spring force means providingspring forces coordinated with the magnetic forces so as to provide thefirst basic stable position of said magnetic bar means corresponding tosynchronous positioning of said valve means within predetermined limits,and the magnetic forces effective on said magnetic bar means overcomingthe spring forces in response to asynchronous movement of said valvemeans to provide two stable disturbance positions for said magnetic barmeans.
 22. A monitoring device according to claim 21, further comprisingswitching means effective for returning said magnetic bar means from oneof the stable disturbance positions thereof to the first basic stableposition thereof.
 23. A monitoring device according to claim 22, furthercomprising electromagnetically actuated auxiliary control valve meansfor said valve means, and said switching means for returning saidmagnetic bar means to the first basic stable position thereof includes ashort-circuit switch means for bridging said switch means responsive tosaid plungers and arranged in the circuit means of said auxiliarycontrol valve means.